Book	FZJ-2013-03568

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png An analysis of the global atmospheric methane budget under different climates

Basu, A. (Corresponding author)FZJ*

2013
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-859-4

Please use a persistent id in citations: http://hdl.handle.net/2128/5267

Abstract: Methane is the second most important gas after CO$_{2}$ in the atmosphere in terms of radiative forcing. It also plays an important role in tropospheric chemistry and influences the oxidation capacity of atmosphere and amount of CO, O$_{3}$ and water vapour. Various biogenic and anthropogenic sectors including gas and oil extraction, wetlands, animal ruminants emit methane in the atmosphere while it is mainly OH which displaces it. At present, the mean global methane concentration is balanced approximately at 1780 ppb after undergoing several changes over the past decades. The sources and sinks currently contribute between 450 and 510 Tg per year although the strength of each source components suffers from uncertainty. Methane is also assumed to be a key player in past climatic changes and its global abundance underwent several transitions which were recorded in the ice cores. One of the drastic changes in methane mixing ratio is observed during the last glacial-interglacial transition, as it shows an increasing trend from 350 ppb till it reaches 700 ppb at the pre-industrial Holocene. The post industrial increase in global methane concentration is also unprecedented. In this study, methane distribution at present climate as well as at Last Glacial Maximum (LGM) and pre-industrial era is simulated with a simplified global tropospheric model ECHAM MOZ. For this simulation, methane emissions from various inventories have been used. A new parameterisation method is developed to estimate wetland methane emission for present day which is later adapted for LGM and pre-industrial time. Wetlands are the largest natural source of methane, still suffers from huge uncertainties. Contrary to the other hydrological models, the present wetland parameterisation follows a simplified approach based on a handful of soilparameters from CARAIB vegetation model. This method is easily adaptable to past climate simulations. The model result for present day from ECHAM MOZ chemistry simulation has been validated with station observation data across the globe and a set of sensitivity analysis with the modified sources are carried out to optimize the global methane budget. One of the major findings from this study is the optimized wetland methane strength which falls in the lower range of IPCC AR4 report. The ECHAM MOZ transient simulation could produce the recent methane trend and inter annual variability between 1990 and 2006 reasonably well although shows an underestimation in a range of 20-40 ppb for the first eight years. This is perhaps caused due to the underestimation of the oil and gas extracted methane source used in the model. For LGM and pre-industrial period, the model, using my wetland methane source successfully reproduces the ice core methane records. Compared to previous studies, the present LGM model source strengthis weaker which raises the possibility of a less deviated sink than present. This is supported by some recent studies on the tropospheric oxidative chemistry which found less OH variability than previously assumed. The important aspect of the present study is that contrary to previous studies where sinks are often hold responsible to explain atmospheric methane variability, here the emphasis has been given to the role of changing source based on these recent findings.

Keyword(s): Dissertation

Note: Universität Köln, Diss., 2013

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Contributing Institute(s):

1. Troposphäre (IEK-8)

Research Program(s):

1. 233 - Trace gas and aerosol processes in the troposphere (POF2-233) (POF2-233)

Appears in the scientific report 2013

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Database coverage:

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